Package org.apache.commons.collections4.list

Class SetUniqueList<E>

  • All Implemented Interfaces:
    Serializable, Iterable<E>, Collection<E>, List<E>
    public class SetUniqueList<E>
extends AbstractSerializableListDecorator<E>
    Decorates a List to ensure that no duplicates are present much like a Set.

    The List interface makes certain assumptions/requirements. This implementation breaks these in certain ways, but this is merely the result of rejecting duplicates. Each violation is explained in the method, but it should not affect you. Bear in mind that Sets require immutable objects to function correctly.

    The ListOrderedSet class provides an alternative approach, by wrapping an existing Set and retaining insertion order in the iterator.

    This class is Serializable from Commons Collections 3.1.

    Since:
    3.0
    See Also:
    Serialized Form

    • Constructor Detail

      • SetUniqueList

        protected SetUniqueList​(List<E> list,
                        Set<E> set)
        Constructor that wraps (not copies) the List and specifies the set to use.

        The set and list must both be correctly initialised to the same elements.

        Parameters:
        set - the set to decorate, must not be null
        list - the list to decorate, must not be null
        Throws:
        NullPointerException - if set or list is null

    • Method Detail

      • setUniqueList

        public static <E> SetUniqueList<E> setUniqueList​(List<E> list)
        Factory method to create a SetList using the supplied list to retain order.

        If the list contains duplicates, these are removed (first indexed one kept). A HashSet is used for the set behaviour.

        Type Parameters:
        E - the element type
        Parameters:
        list - the list to decorate, must not be null
        Returns:
        a new SetUniqueList
        Throws:
        NullPointerException - if list is null
        Since:
        4.0

      • asSet

        public Set<E> asSet()
        Gets an unmodifiable view as a Set.
        Returns:
        an unmodifiable set view

      • add

        public boolean add​(E object)
        Adds an element to the list if it is not already present.

        (Violation) The List interface requires that this method returns true always. However this class may return false because of the Set behaviour.

        Specified by:
        add in interface Collection<E>
        Specified by:
        add in interface List<E>
        Overrides:
        add in class AbstractCollectionDecorator<E>
        Parameters:
        object - the object to add
        Returns:
        true if object was added

      • add

        public void add​(int index,
                E object)
        Adds an element to a specific index in the list if it is not already present.

        (Violation) The List interface makes the assumption that the element is always inserted. This may not happen with this implementation.

        Specified by:
        add in interface List<E>
        Overrides:
        add in class AbstractListDecorator<E>
        Parameters:
        index - the index to insert at
        object - the object to add

      • addAll

        public boolean addAll​(Collection<? extends E> coll)
        Adds a collection of objects to the end of the list avoiding duplicates.

        Only elements that are not already in this list will be added, and duplicates from the specified collection will be ignored.

        (Violation) The List interface makes the assumption that the elements are always inserted. This may not happen with this implementation.

        Specified by:
        addAll in interface Collection<E>
        Specified by:
        addAll in interface List<E>
        Overrides:
        addAll in class AbstractCollectionDecorator<E>
        Parameters:
        coll - the collection to add in iterator order
        Returns:
        true if this collection changed

      • addAll

        public boolean addAll​(int index,
                      Collection<? extends E> coll)
        Adds a collection of objects a specific index in the list avoiding duplicates.

        Only elements that are not already in this list will be added, and duplicates from the specified collection will be ignored.

        (Violation) The List interface makes the assumption that the elements are always inserted. This may not happen with this implementation.

        Specified by:
        addAll in interface List<E>
        Overrides:
        addAll in class AbstractListDecorator<E>
        Parameters:
        index - the index to insert at
        coll - the collection to add in iterator order
        Returns:
        true if this collection changed

      • set

        public E set​(int index,
             E object)
        Sets the value at the specified index avoiding duplicates.

        The object is set into the specified index. Afterwards, any previous duplicate is removed. If the object is not already in the list then a normal set occurs. If it is present, then the old version is removed.

        Specified by:
        set in interface List<E>
        Overrides:
        set in class AbstractListDecorator<E>
        Parameters:
        index - the index to insert at
        object - the object to set
        Returns:
        the previous object

      • retainAll

        public boolean retainAll​(Collection<?> coll)

        This implementation iterates over the elements of this list, checking each element in turn to see if it's contained in coll. If it's not contained, it's removed from this list. As a consequence, it is advised to use a collection type for coll that provides a fast (e.g. O(1)) implementation of Collection.contains(Object).

        Specified by:
        retainAll in interface Collection<E>
        Specified by:
        retainAll in interface List<E>
        Overrides:
        retainAll in class AbstractCollectionDecorator<E>

      • subList

        public List<E> subList​(int fromIndex,
                       int toIndex)

        NOTE: from 4.0, an unmodifiable list will be returned, as changes to the subList can invalidate the parent list.

        Specified by:
        subList in interface List<E>
        Overrides:
        subList in class AbstractListDecorator<E>

      • createSetBasedOnList

        protected Set<E> createSetBasedOnList​(Set<E> set,
                                      List<E> list)
        Create a new Set with the same type as the provided set and populate it with all elements of list.
        Parameters:
        set - the Set to be used as return type, must not be null
        list - the List to populate the Set
        Returns:
        a new Set populated with all elements of the provided List